In recent years, the orthogonal frequency division multiplexing (OFDM) system has become a mainstream communication system in the field of digital communications, and the OFDM system can improve the performance of multiple-input multiple-output (MIMO) networks effectively. However, the conventional orthogonal frequency division multiplexing system requires performing the inverse discrete Fourier transform (IDFT) for several times, thus increasing the computing complexity of the system.
A cyclic-delay diversity orthogonal frequency division multiplexing (CCD-OFDM) system provides a method of transmission diversity capable of converting a multiple-input single-output (MISO) channel into a single-input single-output (SISO) channel by simply performing the inverse discrete Fourier transform (IDFT) operation once, and receivers do not require any additional decoder, and thus the CCD-OFDM system provides a better system than the conventional OFDM system.
A method for optimizing the channel estimation performance applied in a cyclic-delay diversity orthogonal frequency division multiplexing system has been disclosed. For example, “A novel CDD-OFDM scheme with pilot-aided channel estimation,” published by S. Lu and N. Al-Dhahir in IEEE Trans. Wireless. Comm., vol. 8, no. 3, pp. 1122-1127, March 2009 adopts a design of pilots to improve the channel estimation performance. However, this conventional method requires arranging the pilots in different OFDM symbols, and the quantity of transmitting antennas must be equal to the quantity of OFDM symbols before the effect of improving the channel estimation performance can be achieved, and thus there are many limitations in this application. In addition, this conventional method requires a plurality of OFDM symbols for transmitting the pilots, and receivers have to receive many OFDM symbols to perform the channel estimation, thus resulting in a serious delay of the system.
Therefore, it is an important subject for the present invention to provide an orthogonal frequency division multiplexing system capable of simplifying the computing complexity and overcoming the system delay problem in order to provide a better flexibility of the applications.